Tapco Link.FireWire 4x6 Audio Interface Review | MusicRadar
tapco linkfirewire 4x6 audio interface drivers mac os x 10.8 (mountain lion) and later will natively support multiple instances of audio interfaces connected to the same computer. however, you will need to set the input/output devices to 'none' in the sound preferences.
Tapco Linkfirewire 4x6 Audio Interface Drivers
if you're looking to use a firewire 4x6 interface with an older mac, you will need to use an older version of the firewire driver. as always, you should check your computer's system requirements before you buy a firewire 4x6 interface. an example of a firewire 4x6 interface is the apogee onyx-i.
it's just a shame that hardware manufacturers are still hard at work to provide drivers that don't work with mac os. i am not the first to point this out. but for one reason or another, many of these drivers do not work in 10.11 el capitan. if you are interested, check out this thread on the macrumors forum.
very important: for any pci device, there is no such thing as an automatic driver. all drivers have to be installed by hand via a command-line utility provided by the vendor. drivers are usually only provided by manufacturers of specific sound cards/interfaces, and these are usually only compatible with the most recent version of mac os. this means that the problem with 10.11 el capitan is not specific to any particular interface, but rather a result of the required firmware update to newer versions of core audio. this applies to all old mac os versions as well. as far as the ilok software is concerned, it is not a problem with apple's new os. it's a problem with the interface. and the solution to that problem is to find the right driver for your device. so, in order to get work around the current limitations of your interface, you need to have a driver that works with el capitan.